This invention relates to serial binary pulse decoders and, more particularly, to a system for decoding pulse information magnetically recorded on a magnetic tape even while the tape transport speed is increasing or decreasing, and, more particularly, to a system for detecting and decoding serial binary numbers that identify the frames of video information on a video magnetic tape even while the tape is subject to acceleration and deceleration.
Heretofore, the frame numbers on a video magnetic tape that identify successive video frames along the tape have been encoded along the edge of the tape using FM type encoding such as the Manchester or Harvard code. This type of encodement is designed to be used where the binary numbers are detected from the moving tape by a magnetic detecting head and the tape transport speed is substantially constant. In accordance with one encodement of this sort, each frame is identified by a serial binary number made up of successive bit intervals and within each interval, the occurrence of a single pulse represents a binary ZERO for that interval while the occurrence of two pulses represents a binary ONE for that interval. Detection and encodement are accomplished in a relatively conventional fashion when the tape transport speed is substantially constant or changes very little between frame numbers. However, where the tape transport speed changes rapidly during the detection of a single frame number, the time interval between successive binary bits of the number changes so much that the system cannot distinguish between a binary ZERO and a binary ONE by simple comparison. For example, the successive bit intervals decrease when the tape accelerates and increase when the tape decelerates and these decreases and increases are sometimes so large that a simple comparison of each present or current pulse interval with the prior pulse interval to establish the binary sense of the present bit is not reliable.